Apparatus for oxidizing potassium ferrocyanide to potassium ferricyanide



May 16, 1933; R. BRANDT y fw@ API-ARATUS FOR OXIDIZING lOTASSIUM FERROCYANIDE TO POTASSIUM EERRIGYANIDE Filed Aug. 7, 1951 Patented May 16, 1933 UNITED STATES RICHARD BRANDnoF BERGEDORF ivEAn HAMBURG, GERMANY APPARATUS ron oxIniziNG roaassinivr rnnnoevani'nn 'To ro'rassitr'ii l FERRICYANIDE Application led August "7, 17931, lSerial No.555,8`3`6, and in Germany December f8, 1930.V

lytic revivification of the ferrocyanide of potassium formed in the purification of gases by oxidation of the hydrogen sulphide by ferricyanide of potassium to form sulphur and is characterized by the feature that in the anodic oxidation of the ferrocyanide of potassium solution, Which must contain beforehand at least a small Vquantity of ferricyanide of potassium, in electrolytic cells` Without a diaphragm and preferably with electrodes of iron, the caustic potash formed in the electrolysis is converted in the nascent state by alkali metal bicarbonate into alkali metal carbonate.

My present invention relates to an 'improved apparatus for the electrolytic revivification of the ferrocyanide formed in the purification of gases by oxidation of the hyy drogen sulphide by ferricyanide of potassium to form sulphur in electrolytic cells Without a diaphragm.

The present improvement or modification resides in the feature that the battery formed after the fashion of a filter press and serving '30 for the anodic oxidation is formed of bipolarly acting plates Which consist of alloysv of iron With chromium and nickel (so called V2A metals).

liydroeyanic acid along With hydrogen sulphide etc., an electrode material consisting substantially of iron cannot be used With 4 special advantage. If, for example, Water gas, which contains only about 6 to 9 grams of hydrocyanic acid in 100 cubicmetres Yof gas, is to be freed from sulphur according to the prior process, then While observing the other steps of the operation characterized in the prior patent there are formed on the cathode surfaces and also on the anode surfaces of the battery more or less thick covering layers which With continuous loading ofV the battery lead to undesirable increase of the terminal voltages. As the :cause of this there is to #be-considered above-'all the circumstance that anoclic-al-ly a certainaction 'on iron ("even cast iron) occurs, whereby the Washing-'liquid is lenriched With iron. If 55 sufficient hydrocyanic acid is present `in the gas, as is the case, for example, with coal distillation gases, this 'iron which com-es anodically into solution is converted by :aid of the potash contained in they'vashing lfiqe- 60 uidinto ferro'cyanide of potassium., 'so that lio-further enrichment can take place. If, however, there is a 'shortage Vof fhydrocyanic acid as, for exainple, in the' `case of WaterAg-as, there oc'cuisa certain supersaturation of the 65 lye with anodically dissolvedfiron, and covering layers accumulate on the electrode rvsurfaces, which layers gradually become thicker and occasion frequentand expensive cleaning of the battery. g '70 The 4drawbacks thus experienced caribe avoided if linstead of'purjefiro'n electrodes there are employed electrodes consisting `of Valloys of iron, for example, With chromium and nickel. practically `useful there have 75 l been' found, for "example, .the V2A inetalsof Vcommerce,containing about% iron, 23%

chromium 4,and 7 %"nickel. With theusejof such iron alloysk a much less an'dic action is to 'be observed than With the use of pure'iron 80 (cast iron). So far as this actioiroccurs to a noticeable extent minimum quantities of liyldrocy'anic Vacid in the gas to :be purified suf- It has been found that in the performance 35 of the process according to the prior patent with gases which contain` only very littleV tice; for; example, such quantitiesfa's are con- 'tainedl in Water gas in ordertoinhibitfthe S5 yformation of-an'odic covering layers, Also in this case the directions given in thexspecificatio-nv of the prior patentk are to be strictly observed according to which the VWashing liquid to'be revivi'fied in the circuit mustfalvvays'jo contain some Vferricyanide. of potassium. Also the 'caustic alkali formediinthe elctrolysis must be 'converted by means of-` bicarbonate into carbonate andthe alkali content of the Washing liquid correspondingly'195 -adjusted f v Y Y The Washing liquid. containsadvantageously along With-20% to 2,5% ferro'cyanide 'of :potassiumabout Ll'Z/O-to 6%,of potassium carb'onateand bicarbonate. SuchV afiye can be''100 per se.

continuously revivified electrolytically with V2A electrodes even in the treatment, for eX- ample, of water gas, without an appreciable alteration of the loading capacity of the battery with uniform terminal voltage being experienced. The anode surfaces remain per-v fectly blank, while the cathode surfaces are covered with a covering layer whichincreases up to a definite thickness, which layer inhibits cathodic reduction of the anodically formed ferricyanide of potassium and thereby influences very favourably the consumption of current.

vApparatus according to the present invention is illustrated by way of example in the accompanying drawing.

Referring to the drawing there are used V2A electrodes preferably in the form of quadrilateral sheets which may be ribbed for the purpose of increasing the surface. These sheets are assembled to form a battery after the fashion of a filter press in manner known In the embodiment illustrated there are twelve sheets 1 to 12y arranged in two groups. The sheets are held together by two end plates S1, S2. Between the sheets are distance 0r packing pieces of rubber which are located near the edges of the sheets and compressed by the plates S1 and S2. Fitted to the plates S2 and S2 are conduits 13 and 14 through which the washing liquidV to be reviviiied flows into thel apparatus.

- liquid passes first to two distribution pockets Tl and T2 formed in or on the end plates S2, S2. From these pockets the electrolytic liquid flows through openings O provided in the l sheet first into the outer chambers Kl or K1 and then in series in the direction of the ar which the liquid Hows through the outlet con- 4 'duit 15. The hydrogen evolved in the electrolysis also flows into this central chamber M from which it flows off upwardly through the tube 16 after separation from the lye.Y

The hydrogen flows through separate holes O1 provided in the sheets to the central cham- Aof the lye. Y

The supply of current to such a battery is Y ber.l V'These holes O1 lie somewhat above Vthe upper openings O serving for the passage effected preferably at the end plates 1, 12.

The two middle sheets 6 and 7 defining the central chamber M are bridged as shown at They act, therefore, exactly like the end plates 1, 12 in'contrast with the other sheets rocyanide to potassium ferricyanide compris-V 3 to `5 and 8`to 11 as one-sided electrodes.

I claimzv f An apparatus for oxidizing potassium fering a battery` formed'after the fashion of a Vfilter press and serving for they-anodic omdal tion, saidy batteryA having-'bipolarly acting electrode plates consisting of alloys of iron with chromium and nickel, said electrode plates being packed at the edges by rubber packing pieces for forming chambers between said plates, said electrode plates being further provided with openings alternately at the top and bottom permitting the passage of the washing liquid, a central chamber between two innermost plates and top openings in said innermost plates permitting the passage of the hydrogen evolved into the said central chamber.

In testimony whereof I have signed my name to this specification.

RICHARD BRANDT.

The l. 

